230 THE ANATOMY OF VEETEBEATED ANIMALS. 



There were strong ribs, laiit nothing is known with cer- 

 tainty of the sternum, limb-arches, or other bones. 



The veiy complete specimens of the skull that have been 

 discovered prove that its structure was veiy similar to that 

 of the Old World Monitors in the large size of the nasal 

 apertures, and the fusion of the nasals into a narrow bone. 

 But sharp recurved teeth are ankylosed by theii- bases, 

 not only to the premaxillary, maxillary, and dentary bones, 

 but also to the pteiygoid bones ; and these pterygoid 

 lx)nes are unlike those of other Lacertilia, not only in 

 form, but l>ecause they articulate together in the middle 

 Une for a considerable distance behind the posterior nasal 

 apertui-e. 



12. Tlie Amphisbcenoida. — These lizards have completely 

 snakeUke bodies; one genus of the gi'oup {Chirotes) has 

 a pair of small pectoral members, but the rest are apodal. 

 The integument of the body is not scaly, but its sm-face is 

 divided into small rectangular arese arranged in transverse 

 rows. The tail is exceedingly short, so that the vent is 

 close to the end of the body. 



The numerous proccfilous vertebras have less elliptical 

 articular faces than those of the typical Lacertilia. There 

 is no sacrum, and all the precaudal vertebrae, except the one 

 or two of the most anterior, have ribs. The representatives 

 of the chevron bones in the tail are firmly imited with the 

 centra of the vertebras. The vertebrae have no zygantrum 

 nor zygosphene. Amphisbcena has no sternxim. Chirotes has 

 a sternum, but it is not united with the ribs. 



The skull, unlike that of Lacertilia in general, developes no 

 interorbital septum. In this respect, and in the complete 

 closui-e of its anterolateral walls by bone, it resembles the 

 Ophidian cranium. There is no colirmella. Postfrontals 

 are absent, and the squamosal is very small. The quadrate 

 bone is small, and inclined not only downwards, but for- 

 wards, in a manner unknown in other Lacertilia. The two 

 rami of the mandible are firmly united by suture. 



In Atnphishoina the premaxillse bear two rows of teeth. 



